Aqueous Zinc Batteries with Ultra-Fast Redox Kinetics and High Iodine Utilization Enabled by Iron Single Atom Catalysts

Highlights The porous structure and interconnected conductive pathways accommodate a large amount of iodine, entrap polyiodides and guarantee its efficient utilization. While the Fe single atom catalyst efficiently catalyzes the iodine/polyiodide conversion. With “confinement-catalysis” host, the ZnǀǀI2 battery delivers a high capacity of 188.2 mAh g−1 at 0.3 A g−1, excellent rate capability with a capacity of 139.6 mAh g−1 at 15 A g−1 and ultra-long cyclic stability over 50,000 cycles with 80.5% initial capacity retained under high iodine loading of 76.72 wt%. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01093-7.

S2/S11 magnetic stirring for 180 min. After lyophilization, the resultant power is ground in a mortar, then heated at 800 °C under a nitrogen atmosphere for 1 h. This is followed by heating in ammonia gas at 800 °C for another 15 min in a tube furnace. After this ammonolysis step, the sample of Fe SAC-MNC is cooled to room temperature under a N2. As same as the preparation of Fe SAC-MNC, MUiO is heated under N2 and NH3 flow, but without Fe complex solution.

S1.1.3 Preparation of Fe SAC-MNC/I2, MNC/I2 and Ketjen Black/I2 (KB/I2) Frameworks
In melt diffusion method, the iodine is infiltrated into the pores of Fe SAC-MNC host. Fe SAC-MNC powder (50 mg) is mixed together with I2 (200 mg) in an agate mortar. The mixture is sealed in a hydrothermal synthesis reactor and heated at 120 °C for 12 h and then at 80 °C for 12 h to generate the Fe SAC-MNC/I2 framework. Similarly, MNC/I2 and KB/I2 frameworks are fabricated using above melt diffusion method.

S1.2 Materials Characterization
Transmission electron microscopy (TEM) images on a Talos F200X operating. Double Cs Corrector Transmission Electron Microscope (Themis Z) is used to verify single atom sites. X-ray diffraction patterns (XRD) are collected on a X'Pert PRO X-ray diffractometer equipped with a Cu Kα radiation source. Raman spectra are collected on a Renishaw in Alpha300R spectrometer at an excitation wavelength of 514 nm. X-ray photoelectron spectroscopy (XPS) measurements are carried out on a spectroscopy (Axis Supra, Kratos). The specific surface area is obtained via Brunauer-Emmett-Teller (BET) method using desorption data and the pore size distribution is derived from the adsorption branch by using the Barrett-Joyner-Halenda (BJH). TGA is carried out on a thermal analyzer, NETZSCH STA 449F3 at 30-500 °C with an N2 flow of 60 mL min -1 . Electrochemical measurements. UV-vis diffuse reflectance spectra are examined by a spectrophotometer (LAMBDA 365).

S1.3 Computational Details
All the calculations are performed based on spin-polarized first-principles density functional theory (DFT) using the projector augmented-wave method as implemented in the Vienna ab initio Simulation Package (VSAP) [S1, S2], which contains the generalized gradient approximation (GGA) [S3] of the Perdew-Burke-Ernzerh (PBE) functional. The plane-wave-basis for the reciprocal space set with a cutoff of 450 eV is used. The convergence criteria for energy and the residual force are less than 10 -5 eV and 0.05 eV Å -1 . Only the gamma point is used for sampling the first Brillouin zone. The DFT-D3 correction method proposed by Grimme et al. [S4]. is used to accurately describe the vdW interaction by setting IVDW = 11. A vacuum layer with a thickness of more than 20 Å is added to avoid interactions between adjacent cells.
The adsorption energy of X (X = I − , 2

S1.4.1 I2 Reduction Reaction Tests
The three-electrode electrochemical cell with Zn metal as counter electrode and reference electrode, catalyst deposited carbon fiber cloth (CFC) as working electrode. Before electrocatalytic testing, high-purity N2 gas is bubbled through the electrolyte for over 10 min to remove the dissolved O2. The electrochemical accessibility of the working electrode is optimized by potential cycling between 1.0 and 1.6 V at 1 mV s -1 in 2 M ZnSO4 solution with 0.02 M I2 added until stable CV curves are obtained.

S1.4.2 Nucleation of I2 on Fe SAC-MNC, MNC and KB
The 2 M ZnSO4 solution with 0.2 M I3added is used as catholyte. Fe SAC-MNC, MNC or KB is used as the cathode and zinc metal as the anode. 75 μL amount of 2 M ZnSO4 solution with 0.2 M I3added is added to the cathode side. 75 μL amount of 2 M ZnSO4 solution is added to the anode side. The cells keep potentiostatically discharged at 1.34 V (vs. Reference electrode) to ensure I2 nucleate.

S1.4.3 Electrochemical Tests
Typically, the active materials are mixed with Ketjen Black and polyvinylidene fluoride (PVDF) with a weight ratio of 7:2:1. Then, the mixture is dispersed in a small methyl-2-pyrrolidinone (NMP) solvent by grinding in an agate mortar to achieve a stably homogeneous paste. After that, the paste is painted on carbon paper and dried at 40 °C for 8h under vacuum environment. The loading mass is about 1.2-1.8 mg cm -2 . The battery is constructed with as-above synthesized electrode as cathode, glass fiber as separator and metallic Zn foil as anode in CR2032 coin cells. We use 2 M ZnSO4 aqueous solution with 0.04 M I3added as electrolyte. The CV curves are carried out using CHI 760D workstation (Chenhua, China). The electrochemical workstation (CS2350M) was employed to record the electrochemical impedance spectroscopy (EIS). Galvanostatic cycling studies are performed using LAND battery testing system at room temperature. In GITT tests, the discharge current pulse is set at 56 mA g −1 for 1 min and the battery relax for 30 min to reach voltage equilibrium. This procedure is S4/S11 repeated during the entire discharge process. The diffusion coefficient is calculated from: where τ refers to the duration of the current pulse, ∆Eτ is the potential for this duration, m, V and M are the mass, molar volume (cm 3 mol −1 ) and molecular weight (g mol −1 ) of the active material, respectively. S is the contact area of the electrode in the electrolyte, and; ΔEs is the difference in open circuit voltage, measured at the end of the relaxation period of two successive steps. The equation is simplified in the condition of a linear relationship of dEτ/dτ 1/2 and τ < L 2 /DGITT where L is electrode thickness.

S1.4.4 Pouch-type Batteries Preparation
The active materials are mixed with Ketjen Black with a weight ratio of 7:2. Then, the mixture is blended with PTFE (10%) and Isopropyl alcohol by grinding in an agate mortar to achieve a stably homogeneous paste. The paste is painted on titanium mesh and dried at 40 °C for 8h under vacuum environment to gain cathode. Zinc plate is used as anode. Cathode, glass fiber as separator and anode are compressed in an aluminumplastic pouch, followed by injecting an appropriate amount of 2 M ZnSO4 aqueous solution with 0.04 M I3added electrolyte. After that, we completely enclose the aluminum-plastic pouch.